1. Field of the Invention
The present invention relates to a liquid drop detection method and an apparatus therefor, for detecting liquid such as drops of rain adhering upon a front windshield of an automobile, so as to drive a wiper and so on corresponding thereto.
2. Description of Prior Art
An optical type liquid drop detector (a rain sensor) was already proposed and disclosed in Japanese Laid-Open Patent No. Hei 9-68616 (1997) filed by the inventors of the present invention.
This detector has a construction wherein a light emitting element and a light receiving element are attached on one side surface of a glass plate, and wherein a light beam emitted from the light emitting element is guided into the glass plate through a light guiding body and enters into a light receiving element after undergoing total internal reflection within the glass plate. When such the light beam undergoing total internal reflection within the glass plate enters into the light receiving element, it is reduced in an amount (intensity) by loss from the total internal reflection if water drops are adhered at surface points where the total internal reflection is taking place, thereby enabling detection of the adhesion of water drops on the surface of the glass plate on the basis of the reduced amount of received light.